Method of casting printing-plates.



R. T. JOHNSTON. METHOD OF CASTING PBINTiNG PLATES.

APPLIGATIONI-ILED 001. 21, 1912.

Patented Apr. 7, MM

. ROBERT T. JOHNSTON, OF CHICAGO, ILLINOIS, ASSIGNOR TO THE GOSS PRINTING vPRESS COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS...

METHOD OF GASTING PRIN TIN G-PLATES.

wearer.

To all whom it may concern.

Be it known that I, ROBERT T. JOHNSTON, a citizen oftheUnited States, residing at .Chicago, in the county of Cook and State ate mold, either cast curved for use in that condition or cast flat for use on a fiat-bed press or to be curved by a subsequent operation for use' on a cylinder press. By other processes, a metal printing face is produced in the form of a shell, which shell it is necessary by a subsequent operation to back up properly to strengthen it for use. A much-used method of backing up such a shell comprises the placing of the shell in osition in a casting-box so that the shell itself forms the front face of the plate, the rear, face of which is defined by the back of the casting-box or mold.

* In most cases it is highly important to cool the finished printing plate as rapidly as is consistent with good workmanship. However, it has always been found necessary to cool the printing face of a cast plategradually up to a certain well-recognized limit in order to prevent a ,distortion of the figures upon the plate such as to render the v plate imperfect or even useless. It has therefore been the practice to protect the face of the plate against rapid cooling, while at the same time the back of the plate has been cooled much more rapidly. v To this end, the back of the casting box or mold has been formed of metal, usuallyiron, arid steps have'been taken to-bring about a rapid cooling of the back of the casting box, very often by the expedient of forcing water into contact with the back of the casting box. The result of this has been that the back,

of the plate so chilled has had a. mottledv appearance and has shrunk irregularly so as to produce a varied thickness through the plate. To bounteract this irregularity in thickness, in order that the platemight be Specification of Letters Patent.

Application filed October 21, 1912.

Patented Apr. '71, 1914. Serial No. 726,976.

of the required thickness so as to bring the printing face of the plate precisely at the desired point when the plate is appliedto a press, it has been customary to provide the back of the plate in casting with a plurality of ribs by reason of which the eli'ective thickness of the plate has been made slightly greater than the desired thickness. Then by a subsequent operation the ribs have been planed or shaved ofi to bring the effective thickness of the plate to precisely the dimensions desired. 7

It is the object of this invention to improve the processes ofproducing printing plates in-su-ch a manner as to insure that the plate shall be of the desired eifective thickness as originally cast and so render the planing or shaving of the back ofthe plate or of the ribs thereof unnecessary.

I It is a further object of this invention to provide means by the use of which a plate may be cast of the desired effective thickness without the necessity for the shaving operation.

I have/accomplished the objects I seek by the expedient of protecting the faces of the 'ribs of the newly-cast plate so that they are not permitted to cool so rapidly as to render them uneven and unreliable. This I accomplish by cutting'the grooves in the back of the casting-box or mold consider ably deeper than is necessary for the for mation of the'ribs on the back of the plate, and by-providing each of such grooves with a member composed of material which is a very poor conductor of heat, the poor heatconducting member of course being proport-ione'd so as tosecure the desired aggregatethickness of the plate and the ribs thereon.

The particular embodiment ofthe apparatus by which I have accomplished these objects is illustrated in the drawings and hereinafter specifically described.

That which I believe to be new is set forth in the claims. 1

The drawing is acrosssectional view of the back of a casting-box and a printing plate in position-thereagainst, partly broken away, the same being an embodiment of the preferred form of my invention.

In this drawing, 10 indicates a metal plate forming the back of a'casting-box, provided with heat radiating ribs 11 on its outer face. 12 indicates a plurality of grooves in the innerface of said plate. 10, said grooves be ing almost completely filled by the blocks of poorheat-conducting material 13. letindicates a printing plate, the upper printing face or which is produced in any 5 suitable "manner.

lo'indieates the ribs formed on the of the printing plate 14.- against the faces of the poor heat-conducting members 13;

As will be readily understood, when the molten printing plate metal is poured into the casting-box, that portion of the molten metal which comes in contact with the metal plate 10 willbe readily cooled by reason of the fact that such plate 10 is a very good conduetor'of heat. But the faces of the ribs 15 cannot be so readily cooled by reason of the fact that the members 13 are poor con ductors of heat. It therefore follows that, while the printing plate 14E as a whole can be cooled almost rapidly as though the mom-- bers 13 were not employed, the'cooling of thefaces of the ribs 15 is very materially retarded and rapid cooling of such faces is prevented. The result is that the ribs 15 do not become cold-shot, or chilled, or mottled in appearance, in the manner above described which is obj ectionablefor the reasons above stated, but the cooling is caused. to proceed more slowly at such a rate that '30 the metal shrinks evenly. In case the members 13 are all located and proportioned so that their faces are at the same distance from the printing face of the plate produced, it follows that the aggregate thickness 36 of the printing plate 14 and the ribs 15 is -uniform throughout the plate 14:, and in case" Y the proportions are such as to produce a plate 14 the effective thickness of which, that is to say, theaggregate thickness of the 40 plate proper and of the ribs-conforms to the. thickness of plate desired'for use on a press, thenit follows that there is no need for shaving the ribs of the printing plate after it is' removed from the casting-box.

-15 By reason of this invention, doing away p with the necessity for shaving the ribs of the plates produced, a very material savingot time in the preparation of a plate is, offooted, which, as said above, is of very great importance, especially. in the preparation of the plates for the run of a daily newspaper.

While I have shown the preferred form of device for practising the method above set forth, it will'be understood that I do not wish to restrict myselfto the form shown except as hereinafter specifically claimed. So far as I am aware, it is new in the art to protect the part of the cast plate which is to serve as a bearing for the plate upon a press against rapid cooling, and my claims are to be construed accordingly.

What I claim as my invention and desire to secure by Letters Patent is, p 1. The method of casting a printing plate, which comprises retarding the cooling of the portion of the plate which forms a bearing for the plate upon a press.

The method of casting a printing plate, which comprises protecting the portion of the plate which forms a bearing for the plate upon a press against rapid cooling.

3. The method of casting a printing plate, which comprises cooling the major portion of the back face of the plate and retarding the cooling of the portion of the plate which forms a bearing for the plateupon a press;

4:. The method of casting a printing plate, a portion only of the back face of which forms the bearing for the plate upon a press, which comprises cooling the back face of said plate with the exception of said bearing portion and retarding the cooling of said bearing portion.

5. The method of casting a printing plate having projecting portions on its back face which form the bearing for the plate upon a press, which comprises retarding the cool-- ing of the bearing faces of said projecting portions and cooling the remainder of the back oi said plate.

6. The method of casting a printing plate having ribs on its back face, which comprises retarding the cooling of said ribs.

7. The method of casting a printing plate having ribs on its back face, which comprises protecting. the faces of said ribs against rapid cooling;

8. The method of casting a printing plate having ribs on its back face, which comn'ises protecting the faces of said rlbs againshrapid cooling and at the same time cooling the remainder of the back face of sald plate.

ROBERT T. JOHNSTON.

lVitnesses 2 I W. H. DE .BUSK,

W. A. FURNNER. 

